The present invention relates to optical solar reflectors for earth satellites.
Most satellites which operate in earth-o-bit require some form of environmental control to maintain a thermal balance between the satellite components and the extremes of the low temperature space background and the radiative flux from the sun. These satellites employ a variety of standard techniques including thermal control coatings, radiators and multilayer insulation (MLI) to achieve this thermal balance. These thermal control systems utilize a variety of materials depending upon application and configuration but they generally have similar properties of lightweight, low outgassing, and high UV stability. Consequently, most of the subsystems have not been designed with any need for very high temperature stability.
With the advent of ground and spaceborne High Energy Laser (HEL) threats, most of the standard materials and techniques commonly used become vulnerable to severe degradation resulting from the high flux and fluence levels. As a result, active and passive countermeasures such as evasive actions or higher temperature materials must be used to withstand or avoid this new environment.
A common technique for obtaining stable, low solar absorptivity to emissivity ratios (.alpha..sub.s /.epsilon.) has been the Optical Solar Reflector (OSR). Typical values of .alpha..sub.s /.epsilon. are 0.08/0.8. The OSR are typically applied in tiles about 1 inch square, consisting of 6 to 8 mil of high purity fused silica as a substrate with a coating of silver on its rear surface to form a second surface mirror. The tiles are bonded to the radiator surface with an adhesive. Since the OSR has high emittance in the IR region of the spectrum, it inherently absorbs at a longer wavelength (SiO.sub.2 absorbs very strongly beyond 5 .mu.m and heats up rapidly when exposed to laser radiation in this region). Large differences in thermal expansions of silica and silver films cause delamination at the silica/silver interface.
It is therefore an object of the present invention to provide an improved Optical Solar Reflector (OSR).
Other objects, aspects and advantages of the present invention will be apparent to those skilled in the art.